Antimicrobial alkali-silicate glass ceramic and the use thereof

ABSTRACT

The invention relates to a glass ceramic, wherein the initial glass comprises 30–65 percent (by weight) SiO 2 ; 5–30 percent (by weight) Na 2 O; 5–30 percent (by weight) CaO, and 0-15 percent (by weight) P 2 O 5 , and wherein the main crystalline phases comprise alkali—alkaline earth—silicate and/or alkali silicate and/or alkaline earth silicate. The invention is characterized in that either a glass ceramic with a single crystalline phase 1 Na 2 O—2CaO—3 SiO 2  is excluded, or the crystalline size of the glass ceramic is &lt;10 μm, or the weight fraction of SiO 2  is &lt;47%.

The subject of this invention is a glass ceramic with an antimicrobialeffect and/or a glass ceramic powder with an antimicrobial effect. Theinitial glass for the glass ceramic and/or the glass ceramic powdercomprises 30–65 percent (by weight) SiO₂; 5–30 percent (by weight) Na₂O;5–30 percent (by weight) CaO, and 0–15 percent (by weight) P₂O₅.

L L. Hensch, J. Wilson: An Introduction to Bioceramics, World ScientificPubl., 1993, describes glass that has a bioactive and partiallyantimicrobial effect as a bioglass. Such bioglass is characterized bythe formation of hydroxyl apatite layers in aqueous media. Heavymetal-free alkali—alkaline earth—silicate glasses with antimicrobialproperties are described in the DE-A-199 32 238 and DE-A-199 32 239patent applications.

U.S. Pat. No. 5,676,720 discloses a glass powder that comprises 40–60percent (by weight) SiO₂, 5–30 percent (by weight) Na₂O, 10–35 percent(by weight) CaO, and 0–12 percent (by weight) P₂O₅; furthermore, thispatent also discloses glass ceramic that are made of a glass of thiscomposition. However, U.S. Pat. No. 5,676,720 does not provide anyinformation regarding the crystalline phase.

U.S. Pat. No. 5,981,412 describes a bioactive bioceramic material formedical applications with the crystalline phase Na₂O—2CaO—3SiO₂. Thecrystallite size is around 13 μm. The ceramization is performed byannealing for nucleation and crystallization. The main focus is onmechanical properties such as K_(1c). The crystalline phase portion isbetween 34 and 60 percent (by volume). U.S. Pat. No. 5,981,412 describesonly a crystalline phase that is a high-temperature phase and that formsonly under the special conditions indicated in this patent.

The technical task of the present invention is to provide a glassceramic and/or powder made of such a glass ceramic that—as well asantimicrobial properties—also exhibits inflammation-inhibiting,skin-regenerating, and light-scattering properties.

The invention resolves this task by providing a glass ceramic inaccordance with claim 1, wherein the main crystalline phase consists ofalkali—alkaline earth—silicates and/or alkaline earth—silicates and/oralkali—silicates.

The glass ceramic and/or the glass ceramic powder as designed by thisinvention are characterized in that in the visible wavelength range theymanifest a defined scattering and reflection effect. In cosmeticapplication, this effect can diminish the visual appearance of skinwrinkles. Furthermore, towards bacteria, fungi and viruses the glassceramic demonstrates a biocidal and, definitely, a biostatic effect.However, in contact with humans, the glass ceramic is compatible withskin and is toxicologically harmless.

When used in the cosmetic field, the glass ceramic as designed by thisinvention has a maximum concentration of heavy metals of, for example,for Pb<20 ppm, Cd<5 ppm, As<5 ppm, Sb<10 ppm, Hg<1 ppm, Ni<10 ppm.

The initial unceramized glass that is used to produce the glass ceramicas designed by the invention contains between 30 and 65 percent (byweight) of SiO₂ as the network-forming ion. With a lower concentration,the propensity for spontaneous crystallization strongly increases, andthe chemical resistance strongly decreases. With higher SiO₂ values, thecrystallization stability level can decrease, and the processingtemperature can grow significantly, so that the hot-forming propertiesdeteriorate. In addition, SiO₂ is also a part of the crystalline phasethat arises during the ceramization and must be contained in the glassin an accordingly high concentration if a high crystalline portion is tobe created by the ceramization process.

Na₂O is used as the fluxing agent during the melting of glass. With aconcentration of less than 5%, the melting process is negativelyaffected. Sodium is a part of the phases that form during theceramization process, and thus must be contained in the glass inaccordingly high concentrations if a high crystalline portion is to becreated by the ceramization process.

K₂O acts as a fluxing agent during the melting of glass. Also, potassiumis released in aqueous systems. If potassium is contained in the glassin a high concentration, potassium-containing phases such as potassiumsilicates are also released. The K₂O content can lie in the range of0–40 percent (by weight), and preferably in the range of 0–25 percent(by weight), and especially preferred is the range of 0–10 percent (byweight).

The chemical resistance of the glass, and thus the ion release inaqueous media, is controlled by the P₂O₅ content. The P₂O₅ content isbetween 0 and 15 percent (by weight). With higher concentrations ofP₂O₅, the hydrolytic resistance of the glass ceramic diminishes to aninsufficient level.

In order to improve its meltability, the glass can contain up to 5percent (by weight) of B₂O₃.

In order not to reach too great a degree of chemical resistance, thequantity of Al₂O₃ should be less than 3 percent (by weight). Al₂O₃ isused to control the chemical resistance of the glass.

In order to enhance the antimicrobial, and especially the antibacterialproperties of the glass ceramic, ions with antimicrobial effects such asAg, Au, 1, Ce, Cu, Zn, Sn, can be incorporated in concentrations lowerthan 5 percent (by weight) or lower than 2 percent (by weight).Especially preferred is the addition of Ag. This allows for theformation (in the glass) of especially preferred crystalline phases,such as silver phosphates, e.g., AgPO₃ or silicon phosphates SiP₂O₇.

Furthermore, ions such as Ag, Cu, Au, and Li, can be incorporated asingredients in order to control the high temperature conductivity of themolten charge, and thus to improve its meltability by means of ahigh-frequency melting process.

The concentration of these ions should be lower than 5 percent (byweight).

Coloring ions such as Fe, Cr, Co, and V can be incorporated,individually or in a combined fashion, in a total concentration of lessthan 1 percent (by weight).

The glass ceramic as designed by the invention is usually used in powderform. The ceramization can be done in the form of a glass block, a glassribbon, or a glass powder. After ceramization, the glass ceramic blocksor ribbons must be ground to powder. If the powder has been ceramized,it must usually be ground again in order to eliminate agglomerates thathave arisen during the ceramization process.

The decisive advantage of the ceramization in the powder form is a verysmall crystallite size that retains high overall phase portions. Inaddition, the crystallites grow from the surface of the surface defectsthat are produced by grinding.

The grinding process generates a large number of surface nuclei, so thatmany crystals start to grow at the same time, which allows one to obtaina very small crystallite size and, at the same time, a high crystallinephase portion. Therefore, no additional annealing treatment, as has beendescribed in the U.S. Pat. No. 5,981,412 patent, is required to generatenuclei.

The grinding process can occur in dry, aqueous, or non-aqueous media.

Normally, the particle size is less than 500 μm. A useful particle sizeis <100 μm or <20 μm. Particle sizes that are <10 μm and smaller than 5μm and smaller than 2 μm are especially useful. The particle size <1 μmhas turned out to be exceptionally suitable.

In order to achieve certain effects, mixtures of various glass powdersof different compositions from the indicated composition range and withdifferent grain size are possible.

If a block or a ribbon of the initial glass is ceramized, and ifcrystalline portions of more than 30 percent (by weight) are endeavored,the crystallite sizes are larger than 10 μm. The crystallization occursvery quickly. The ceramization temperatures are between 50° C. and 400°C. above the glass transition temperature, and are preferably between50° C. and 200° C. above the glass transition temperature, and are alsopreferably within a range of 50° C. and 100° C. Ceramization can be alsoperformed in a multiple-stage thermal process. The crystallizationprocess is primarily controlled from the surface. Needle-shaped crystalsgrow from the surface into the glass inside. A few crystals begin togrow in the glass inside. They are spheroidal. Needle-shaped crystalsarise during the ceramization of a powder because of the large surfacethat is used for this process.

The ceramization of the initial glass is controlled from the surface.If, before the ceramization, the ribbons or blocks of the initial glassare ground into powder, the crystallization temperatures decreasesignificantly. The crystals begin to grow from the surfaces of thepowder particles into their insides. The ceramization process can becontrolled in such a manner that the particles have only an outercrystalline layer, whereas their insides remain amorphous. The selectionof the particle size determines the mean crystal size.

The crystal phase portions in the glass after the ceramization aregreater than 5 percent (by weight). Depending on the composition of theinitial glass, up to almost 100 percent (by weight) of crystalline phaseportions are achieved.

The preferred range is a phase portion between 10 and 30 percent (byweight). Even Still more preferable is the range above 50 percent (byweight).

The crystallite size of the glass ceramic is <10 μm, the preferred sizeis <5 μm, the especially preferred size is <0.5 μm, and quite especiallypreferred is <0.1 μn.

Depending on the ceramization temperature, the ceramized powders arere-ground in order to again dissolve any agglomerations that have arisenduring the ceramization process.

The main crystal phases are alkali—alkaline earth—silicates and/oralkaline earth silicates, especially NaCa silicates and Ca silicates,and these phase portions can be influenced by ceramization.

Other subsidiary crystal phases that can contain silver and/orphosphorus and/or silicon, such as AgPO3, SiP2O7, SiO2, can also occur,depending on the particular composition of the initial glass.

Phosphorus-containing glass ceramics from this range of composition canbe bioactive in aqueous media; i.e., in aqueous systems they can form ahydroxyl apatite layer on their surface and also on foreign surfaces.Such powders are especially suitable as biomaterials, or they can beused in applications in which remineralization processes play animportant role, such as in the fields of hair cosmetics, nail cosmetics,and tooth care.

Using the phases and phase portions, the chemical reactivity and/or theion release can be influenced. Thus, chemical reactivity and ionreleases can be controlled so that the main compatibility, the desiredpH value and antimicrobial level, as well as the inflammation-inhibitingeffect, can be tailored.

The crystalline phases demonstrate a significantly different chemicalresistance than the glass phase. The chemical resistance can be bothincreased and decreased. Aside from chemical properties, depending onthe main crystal phase properties, mechanical, abrasive, and opticalproperties can also be modified.

In the case of glass ribbons, at a relatively low ceramizationtemperature <700° C., first one to two Na—Na silicates are formed. Theseare preferably (Na₂CaSi₃O₈/Na₂CaSiO₄/Na₂Ca₂(SiO₃)₃. Recrystallizationoccurs at temperatures higher than 700° C.

The resultant crystalline phases partially demonstrate a substantiallyhigher water solubility than the glass phase. Thus, a special adjustmentof the phase portions allows one to influence the ion release of thepowder, as well as the pH value in an aqueous solution, and thus thebiological effect.

The light-scattering effects that cause optical effects such astransparency, reflection, and light scattering, are induced by thedifferent refractive indices of the glass phase and the crystal phase,as well as by the existing crystallite size.

During the dissolution of the crystalline phase in water or an aqueoussolution, there remain honeycombed and/or porous surface structures thatparticularly influence the optical properties, such as transmission,reflection, and light scattering, of the powders in formulations. Whensolubilized in aqueous systems, the formation of nano particles isobserved.

The glass ceramic powders are excellently suited for application incosmetic products. Among others, these can be products in the field ofcolor cosmetics. Also, the antimicrobial effect allows for applicationin the field of deodorants and antiperspirants. Moreover, hair and skincare provide other applications within the cosmetic field.

Due to its antimicrobial and inflammation-inhibiting properties, thepowder is also suitable for use as an implant material in the medicalfield and particularly in the field of wound tending.

Furthermore, the material is suitable for use as a carrier substance inthe production of artificial three-dimensional tissue structures.

In addition, the powder can be added to polymers, for example, as anantimicrobial active substance. Furthermore, such glass ceramic powderscan be used in the fields of paints and lacquers, foodstuff, cleaningagents, paper hygiene, medical products, bioproducts, cosmetic products,and oral care.

The invention is described below using design examples and theirattached figures.

FIG. 1 shows an X-ray diffraction diagram of an initial glasscrystallized in powder form with a composition according to the designexample 1, annealed for 5 hours at 650° C.

FIG. 2 shows an X-ray diffraction diagram of an initial glasscrystallized in powder form, annealed for 5 hours at 590° C.

FIG. 3 shows an X-ray diffraction diagram of an initial glasscrystallized in powder form, annealed for 5 hours at 560° C.

FIG. 4 shows a DTA analysis of an initial glass ceramized as a glassblock according to design example 1.

FIG. 5 shows a DTA analysis of an initial glass ceramized in powder formaccording to design example 1.

FIG. 6 shows an X-ray diffraction diagram of glass ribbons ceramized atvarious temperatures according to design example 1.

FIG. 7 shows a high-temperature X-ray diagram of glass powders with aparticle size of approximately 4 μm, depending on the temperature forglass ceramics with an initial glass according to design example 7.

FIG. 8 shows an X-ray diffraction diagram of a crystallized initialglass with a composition according to design example 8, annealed for 4hours at 650° C.

FIG. 9 shows an X-ray diffraction diagram of a crystallized initialglass with a composition according to design example 8, annealed for 4hours at 700° C.

FIG. 10 shows an X-ray diffraction diagram of a crystallized initialglass with a composition according to design example 8, annealed for 4hours at 900° C.

FIG. 11 shows an X-ray diffraction diagram of a crystallized initialglass with a composition according to design example 9, annealed for 4hours at 560° C.

FIG. 12 shows an X-ray diffraction diagram of a crystallized initialglass with a composition according to design example 9, annealed for 4hours at 700° C.

FIG. 13 shows an X-ray diffraction diagram of a crystallized initialglass with a composition according to design example 9, annealed for 4hours at 900° C.

FIG. 14 shows a DTA analysis of a initial glass ceramized as a glassblock according to design examples 8 and 9.

FIG. 15 shows the standardized bacidity for a glass ceramic ceramized atvarious temperatures based on an initial glass with a compositionaccording to design example 1

FIG. 16 shows the standardized conductivity for a glass ceramicceramized at various temperatures based on an initial glass with acomposition according to design example 1

FIG. 17 shows a SEM image of surface crystals on the surface of a glassceramic that has been obtained by annealing an initial glass accordingto design example 1 at 660° C. for 4 hours.

FIG. 18 shows a SEM image of a section through a glass ceramic that hasbeen obtained by means of bulk crystallization by annealing at T=660° C.for 4 hours.

FIG. 19 shows the surface of a glass ceramic ribbon ceramized at 700°C., and subsequently treated with water for 15 minutes.

FIGS. 20A–B show the surface of a glass ceramic ribbon ceramized at 700°C., and subsequently treated in water for 24 hours.

FIGS. 21A–B show the surface of a glass ceramic ribbon ceramized at 900°C., and subsequently treated in water for 24 hours.

A glass was produced by melting raw materials. The melting occurred inplatinum crucibles at a temperature of 1550° C. Subsequently, the moltenmaterial was formed into ribbons. These ribbons were then furtherprocessed by dry grinding into a powder with a particle size of d50=4μm.

Table 1 indicates the composition of the initial glasses in percent (byweight) for all glass ceramics described in the following text.

TABLE 1 Composition (synthesis value) [In percent (by weight)] Ex- ample1 2 3 4 5 6 7 8 9 10 11 SiO₂ 46.0 35 46 50 40 59 45 44.9 35 45 65 Al₂O₃0 0 0 0 0 0 1 0 0 0 0 CaO 25.0 29 20 10 25 20 25 24.5 29.0 23.5 10.0 MgO0 0 0 0 0 0 0 0 0 0 0 Na₂O 25.0 30 20 25 25 20 24 24.5 29.5 24.5 20.0K₂O 0 0 0 0 0 0 0 0 0 0 0 P₂O₅ 4.0 6 0 15 0 1 7 0 0 0 5.0 Ag₂O 0 0 0 0 00 0 0.1 0.1 0 0 ZnO 0 0 0 0 0 0 0 0 0 1.0 0

If we use the initial glasses indicated in Table for the production ofglass ceramics, we discover that the glasses according the designexamples 2 and 9 already demonstrate a strong propensity forcrystallization during the melting process. Therefore, in the case ofthese initial glasses, it is necessary to cool them off especiallyquickly. If a partial or a complete ceramization already occurs duringthe melting of the glass, the glass ceramic can be subjected to a newannealing at the indicated temperatures in order to obtain the crystalphases described in this patent application.

FIGS. 1–3 show X-ray diffraction diagrams of initial glassescrystallized in powder form according to the design example 1 in Table1, annealed for 5 hours at 650° C. (FIG. 1), 590° C. (FIG. 2), and 560°C. (FIG. 3). Clearly recognizable is the decrease in intensity of thediffraction orders 1 related to the crystal phases, which is synonymouswith a decreasing crystal proportion in the glass ceramic.

For example, the intensity peaks can be ascribed to theNa₂CaSiO₄/Na₂OCaSiO₂ and Na₂CaSi₃O₈ crystal phases.

At higher temperatures, a recrystallization occurs, as is apparent fromFIG. 6. At temperatures >900° C., Ca silicates can form, too. FIGS. 4and 5 show the DTA analysis of an initial glass ceramized as a glassribbon according to the design example 1 in Table 1 (FIG. 4), and aninitial glass ceramized in powder form (FIG. 5) with a heating rate of10 K/min. Clearly recognizable is the crystallization peak 3 for thecrystal phase, whose temperatures are lower for the initial glassceramized in powder.

FIG. 5 also shows the slightly exothermal reaction of there-crystallization.

FIG. 7 shows high-temperature X-ray diagrams for a glass ceramic powderthat has been obtained from an initial glass according to the designexample 7, depending on the temperature. Re-crystallization occurs athigher temperatures (over 900° C.). The X-ray measurements were recordedduring the heating process. At these temperatures, Ca silicates can alsoform. FIG. 7 shows 2000.1 and 2000.2, which according to the JCPDSdatabase, designate the Na₂CaSiO₄ phase, and 2002.1 and 2002.2, whichaccording to the JCPDS database designate the Na₂CaSi₃O₈ phase. As isapparent from FIG. 7, the Na₂CaSi₃O₈ phase forms only at a temperatureabove 900° C. The properties of various glass ceramics, produced invarious different ways based on the initial glass according to theexample 1 in Table 1, are indicated in Table 2.

TABLE 2 Properties of glass ceramics according to the design example 1Main Annealing Crystallite crystalline JCPDS time size phases DatabasePowder 580° C. 5 hours <0.5 Na₂CaSi₃O₈/ 12-0671/24- Na₂CaSiO₄ 10696Na₂Ca₂(SiO₃)₃ Powder 650° C. 5 hours <1 Na₂CaSi₃O₈/ 12-0671/24-Na₂CaSiO₄ 10696 Na₂Ca₂(SiO₃)₃ Powder 700° C. 5 hours <15 Na₂CaSi₃O₈/12-0671/24- Na₂CaSiO₄ 10696 Na₂Ca₂(SiO₃)₃ Ribbons 700° C. 5 hours >100μm Na₂CaSi₃O₈/ 12-0671/24- Na₂CaSiO₄ 10696 Na₂Ca₂(SiO₃)₃ Ribbons 600° C.2 hours >20 μm Na₂CaSi₃O₈/ 12-0671/24- in volume Na₂CaSiO₄ 10696Na₂Ca₂(SiO₃)₃

Table 3 shows the antibacterial effect of a glass ceramic powder thatwas annealed at 580° C. for 5 hours with a grain size of 4 μm.

TABLE 3 Antibacterial effect of the powder according to Europ.Pharmakopoe (3. edition): Design example 1 (grain size 4 μm) P. E. coliaeruginosa S. aureus C. albicans A. niger Start 290,000 270,000 250,000300,000 250,000  2 days 900 1,800 800 <100 2,000  7 days <100 200 <100 02000 14 days 0 0 0 0 0 21 days 0 0 0 0 0 28 days 0 0 0 0 0

No irritation has been determined by skin compatibility tests, i.e.,oculsive tests over 24 hours.

Table 4 indicates in detail, and in a tabular form, exemplary maincrystalline phases of Na—Ca silicate systems using the basic formulax Na₂O.y CaO.z SiO₂and the numbers for x, y, and z.

TABLE 4 Main Crystalline phase in Na—Ca silicate systems Na₂O CaO SiO₂(x) (y) (z) 1 3 6 1 1 5 1 2 3 1 — 2 3 — 8 2 3 6 2 — 2 0 1 1 1 0 1

The results of the glass ceramics that have been obtained from theinitial glasses according to design examples 8 and 9 are described inthe following text.

FIGS. 8–10 show the X-ray diffraction diagrams of initial glassescrystallized in powder form according to the design example 8 in Table1, and annealed for 4 hours at 560° C. (FIG. 8), 700° C. (FIG. 9), and900° C. (FIG. 10). The phase determined from the intensity peaks is aNa—Ca silicate, namely Na₆Ca₃Si₆O₁₈ (JCPDS 77-2189) as a crystallinephase. Clearly recognizable is the change of the Na—Ca ratio in tandemwith the increase in temperature.

FIGS. 11–13 show the X-ray diffraction diagrams of initial glassescrystallized in powder form according to the design example 9 in Table1, and annealed for 4 hours at 560° C. (FIG. 11), 700° C. (FIG. 12), and900° C. (FIG. 13). Two Na—Ca silicates Na₂CaSiO₄ (JCPDS 73-1726) andNa₂Ca₂SiO₇ (JCPDS 10-0016), as well as the silicon phosphate SiP₂O₇(JCPDS 39-0189) and cristobalite SiO₂ (JCPDS 82-0512) can be identifiedin FIGS. 11–13 as the main crystalline phases. The samples produced at700° C. and 900° C. that are shown in Tables 12 and 13 contain anothercrystalline phase, namely the silver phosphate AgPO₃ (JCPDS 11-0641).The portion of this phase is higher in the sample produced at 900° C.than in the sample produced at 700° C.

FIG. 14 shows the DTA thermo-analysis of an initial glass ceramized as aglass ribbon according to design examples 8 and 9 in Table 1 withheating rates of 10 K/min. The crystallization peak 3 for the crystalphase is clearly recognizable from design example 8 . The glass ceramicthat is based on the initial glass according to design example 9 is aglass ceramic that has already been crystallized from the molten charge.No strong exothermal signal is observed in the DTA, because thesubsequent crystallization or re-crystallization only releases a littleheat. The reason for this phenomenon is that the initial glass in thisdesign example has a propensity for spontaneous crystallization to occurduring the melting process.

Table 5 shows the antibacterial properties of a glass ceramic powderthat, based on an initial glass according to design example 8, wasannealed at 560° C. with a grain size of 4 μm.

TABLE 5 Antibacterial effect of powders according to Europ. Pharmakopoe(3. edition): Design example 8 annealed at 560° C. (grain size 4 μm) P.E. coli aeruginosa S. aureus C. albicans A. niger Start 290,000 270,000250,000 300,000 250,000  2 days 700 2,000 500 <100 2,000  7 days 0 0 0 00 14 days 0 0 0 0 0 21 days 0 0 0 0 0 28 days 0 0 0 0 0

Table 6 shows the antibacterial properties of a glass ceramic powderthat, based on an initial glass according to design example 9, wasannealed at 900° C. with a grain size of 4 μm.

TABLE 6 Antibacterial effect of powders according to Europ. Pharmakopoe(3. edition): Design example 9 (grain size 4 μm) P. E. coli aeruginosaS. aureus C. albicans A. niger Start 290,000 270,000 250,000 300,000250,000  2 days 0 0 0 0 0  7 days 0 0 0 0 0 14 days 0 0 0 0 0 21 days 00 0 0 0 28 days 0 0 0 0 0

Table 7 indicates, in detail, and in a tabular form, the maincrystalline phases found in the produced samples using the basic formulax Na₂O.y CaO.z SiO₂and the numbers for x, y, and z.

Besides the Na—Ca phases, a silicon phosphate phase is also found. Inaddition, a silver phosphate phase is found at high temperatures above700° C.

TABLE 7 Main crystalline phases of the glass ceramics, design examples 8and 9 Na₂O CaO SiO₂ (x) (y) (z) Ag₂O P₂O₅ Note 1 1 From 700° C. 3 3 6 11 1 1 2 1 1 1 2 1 3

Table 8 indicates the pH values and the conductivity of a 1% suspensionof a glass ceramic powder that comprises an initial glass according todesign example 7 in Table 1, for various annealing conditions for theproduction of glass ceramic. The annealing conditions include annealingtime and annealing temperature. Depending on the annealing time and theannealing temperature, different main crystal phases develop in theglass ceramic.

TABLE 8 pH value and conductivity of a glass ceramic powder that hascrystallized from an initial glass according to design example 7 After15 After 50 After 24 Annealing minutes Conductivity minutes Conductivityhours Conductivity conditions Ph value (μS/cm) Ph value (μS/cm) Ph value(μS/cm) Untreated 11.3 695 11.3 900 11.7 1,872 500° C. - 2 hours 11.1526 11.2 623 11.4 1,054 600° C. - 2 hours 11.2 571 11.2 686 11.5 1,130700° C. - 2 hours 11.2 576 11.2 679 11.5 1,007 800° C. - 2 hours 11.2619 11.3 749 11.5 1,238 900° C. - 2 hours 11.3 859 11.4 949 11.6 1,288

FIGS. 15 and 16 show the pH value, i.e., the standardized bacidity andthe standardized conductivity for a glass ceramic obtained by annealingfor 2 hours at various temperatures based on an initial glass accordingto design example 1.

FIGS. 15 and 16 include the following reference numbers:

-   -   100: The unceramized initial glass according to design example 1    -   102: The initial glass according to design example 1 that has        been ceramized at 600° C. for 2 hours    -   104: The initial glass according to design example 1 that has        been ceramized at 700° C. for 2 hours    -   106: The initial glass according to design example 1 that has        been ceramized at 800° C. for 2 hours    -   108: The initial glass according to design example 1 that has        been ceramized at 900° C. for 2 hours

By standardized bacidity and standardized conductivity, we understandthe bacidity and the conductivity standardized for the surface. Theseproperties are independent of the actual particle size. Conductivity isindicated per surface (cm²) and mass (g) of powder.

Table 9 shows the ion release rate of an unceramized powder and glassceramic powder in a 1% suspension that comprises, as the initial glass,a glass according to design example 7 in Table 1. The glass ceramicpowder has been produced by annealing at a temperature of 650° C. for 4hours.

TABLE 9 Ion release rate (1% suspension, unit: mg/L) Not ceramizedPowder ceramized at 650° C. Na 96.7 mg/Liter 63.2 mg/Liter Ca 29.8mg/Liter 21.5 mg/Liter Si 63.5 mg/Liter 40.3 mg/Liter P 0.22 mg/Liter0.67 mg/Liter pH 11.3 11.3 Conductivity  635 μS/cm  432 μS/cm

The following text describes the scanning of electron micrograph images(SEM images) of glass ceramics that have been obtained by crystallizingthe initial glass according to design example 1.

FIG. 17 shows a SEM image of the surface of a glass ceramic that hasbeen obtained by annealing an initial glass according to design example1 at a temperature of 660° C. for 4 hours. The surface crystals on theribbon are clearly recognizable. Parts of these surface crystals can besoluble in water so that, during a treatment with water, these crystalsare dissolved, and a honeycomb structures remains. Furthermore, thiscrystalline surface can release certain phases, such as nano particlesthat, among other things, are important for applications in oral care,i.e., for the use of glass ceramic as designed by the invention in thefield of tooth and oral care. Furthermore, the crystalline surface shownin this figure demonstrates light-scattering properties that can be usedfor certain applications.

While FIG. 17 shows the surface structure of the glass ceramic, FIG. 18shows a SEM image of the crystallization inside the glass block, thatis, the bulk crystallization. FIG. 17 is a section of FIG. 18. Thesection is marked in FIG. 18 with 3000. The glass ceramic shown in FIGS.17 and 18 has been obtained by annealing [the initial glass] at atemperature of 660° C. for 4 hours. The formed crystallites in FIG. 18are clearly recognizable as round points. The crystals formed in thebulk crystallization have light-scattering properties that can be usedfor certain applications. In FIGS. 17 and 18, crystallization occurredin the glass block (ribbon). Both FIG. 17 and FIG. 18 show across-section of the surface of the block (ribbon). FIG. 17 is a sectionof FIG. 18, and shows the surface in detail.

FIG. 19 shows the surface of a glass ceramic ribbon that has beenobtained by ceramizing an initial glass according to the design example1 at 700° C. for 4 hours. The glass ceramic was subsequently treatedwith H₂O. The easily soluble crystalline phases essentially comprisingNa—Ca silicate are dissolved. There remains a “honeycomb” structure thatcan be easily recognized in FIG. 19.

FIGS. 20A–B show the surface of a glass ceramic powder that has beenobtained by ceramizing an initial glass according to design example 1 at700° C. for 4 hours. The surface shown has been obtained by treating theglass ceramic powder with water for 24 hours.

Furthermore, we can recognize a certain surface coarseness in FIGS. 20Aand 20B. As is apparent from the figures, the surface is relativelyhomogeneous, and does not show any formation of nano particles.

FIGS. 21A–B show the surface of a glass ceramic powder that has beenobtained by ceramizing an initial glass according to design example 1 ata temperature of 900° C. for 4 hours. In contrast to the smooth surfaceobtained at lower annealing temperatures, as shown in FIGS. 20A and 20B,FIGS. 21A and 21B show the released nano crystals and a porous surfacestructure.

The crystalline nano particles are less soluble in water. The nanoparticles were formed during the annealing process, and have beenreleased from the surface.

The released nano particles are important for, among other things,applications in oral care, because they have a desensitizing effect onthe tooth nerve. The desensitizing effect is achieved in that the nanoparticles are able to close the tubulin channels.

The present invention provides a glass ceramic powder and a glassceramic that can be used in a number of fields; for example, in thefields of cosmetics or food supplements, and in the medical field.

1. Glass ceramic formed from an initial glass comprising: 30–65 percent(by weight) of SiO₂ 5–30 percent (by weight) of Na₂O 5–30 percent (byweight) of CaO 0–15 percent (by weight) of P₂O₅, wherein the glassceramic includes crystalline phases comprising at least one silicateselected from the group consisting of alkali metal silicates andalkaline earth metal silicates having a crystallite size <0.1 μm. 2.Glass ceramic according to claim 1, wherein the initial glass comprises:30–<47 percent (by weight) of SiO₂ 10–30 percent (by weight) of Na₂O10–30 percent (by weight) of CaO 2–15 percent (by weight) of P₂O₅. 3.Glass ceramic according to claim 1, wherein the crystalline phasescomprise at least one silicate selected from the group consisting ofsodium silicates and potassium silicates.
 4. Glass ceramic according toclaim 1, wherein the crystalline phases are water-soluble phasescomprising at least one silicate selected from the group consisting ofsodium silicates and calcium silicates.
 5. Glass ceramic according toclaim 1, wherein the initial glass further comprises 0–40 percent (byweight) of K₂O as well as 0–5 percent (by weight) of Al₂O₃.
 6. Glassceramic according to claim 1, wherein the initial glass comprises 0–40percent (by weight) of MgO and 0–50 percent (by weight) of B₂O₃. 7.Glass ceramic according to claim 1, wherein the glass ceramic comprisesions with a total portion of <2 percent (by weight).
 8. Glass ceramicaccording to claim 7, wherein the ions include at least one ion selectedfrom the group consisting of Ag, Au, I, Zn, Cu, and Ce ions.
 9. Glassceramic powder that comprises a glass ceramic according to claim 1,wherein the glass ceramic powder has a particle size of <100 μm. 10.Glass ceramic powder that comprises a glass ceramic according to claim1, wherein the glass ceramic powder has a particle size of <20 μm. 11.Glass ceramic powder that comprises a glass ceramic according to claim1, wherein the glass ceramic powder has a particle size of <5 μm. 12.Glass ceramic powder that comprises a glass ceramic according to claim1, wherein the glass ceramic powder has a particle size of <1 μm. 13.Method for the production of a glass ceramic powder having a particlesize of <100 μm, comprising the steps of providing the initial glass ofclaim 1, grinding the initial glass, and ceramizing the ground initialglass.